The present invention relates generally to two component water-based coatings, inks, adhesives, and sealant compositions and, more particularly, to enhanced molecular weight epoxy emulsions for use in water-based coatings, inks, adhesives, and sealant compositions, and to methods for their manufacture. The present invention also relates to a novel method of curing such enhanced molecular weight epoxy emulsions, and to the novel cured epoxy resins produced thereby.
In one important embodiment, this invention relates to two component water-based "maintenance finishes". Maintenance finishes are water-based coatings which can be applied to previously coated surfaces, to cement and cement block, to plaster, to metals such as steel, and to any other surfaces which are commonly coated with conventional epoxy coatings.
In another important embodiment, this invention relates to two component solvent-free and near solvent-free air dry and heat cure coatings, inks, adhesives, and sealant compositions for application, for example, to metals, to wood, to non-woven as well as woven fabric, and to paper. These coatings, inks, adhesives, and sealant compositions may be used in factory fabrication and factory finishing of such end products as trucks, automobiles, coil aluminum and steel, containers, appliances, tools, doors, windows, siding, paneling, cabinets and shelving, garments, carpets, and such other end uses where appearance, hardness, toughness, chemical resistance, controlled rate of cure, and low VOC (volatile organic compounds) are particularly desirable.
In still another important embodiment, this invention relates to two component water-based coatings which can be applied to asphalt and concrete surfaces as a barrier and containment coating or as a safety marking material or traffic paint.
Environmental considerations have had a profound effect on the use and development of new coatings, inks, adhesives, and sealants, including the organic and inorganic binders which are widely used in them. In confined production lines, for example, electrodeposition, powder, and radiation-cure coatings, adhesives and sealants are increasingly being used to reduce or eliminate VOC concerns. However, large structure applications such as tanks, highways, food and chemical and heavy manufacturing plants cannot benefit from these technologies since they cannot be brought indoors to assembly lines, but rather must be painted in the field.
Two component curable compositions comprising epoxy polymers and polyamine curatives currently are the standard in the art.
The dominant technology in high performance maintenance coatings for such large structure applications is based upon amine cured epoxy coatings. The leader or so-called standard of performance coatings are solvent thinned solid epoxies cured with solvent thinned aminated dimer acids. There are, however, three major objections to such two component systems.
First, there is an objection to atmospheric solvent emissions. In order to dissolve the resins and to reduce the viscosity of formulated materials to application viscosity, large quantities of solvent are required, which may violate applicable emission requirements. Second, there are objections to organic solvents that are used as reducers and thinners, e.g., xylene, toluene, and glycol ethers, which are hazardous chemicals targeted for control or elimination because of their toxicity. Thus, the disclosure of low or no VOC water-borne epoxies to replace the current solvent-based epoxies will not only reduce atmospheric contamination by hundreds of millions of pounds of volatile organic compounds but will simultaneously eliminate the toxic chemical solvents. Third, there is an objection to the lengthy ingestion period and thus lost labor hours required after component mixing in using the current solvent-based epoxies.
Efforts have been made to equal the performance of solvent systems by emulsifying liquid epoxy resins or solvent-thinned solid resins and to cure them with emulsified or water-soluble amines. These efforts have met with limited success, at best, due to problems encountered on both the epoxy side and the amine side of such systems.
On the epoxy side, there are molecular weight and molecular configuration limitations. Solid epoxy resins in the molecular weight range of about 800 are necessary to achieve desired performance properties when amine cured coatings are prepared under ambient conditions, to achieve desired performance properties. Liquid resins with molecular weights in the range of about 390 and cured with similar amine technology simply will not yield the desired performance properties. Further, the molecular configuration is limited to relatively few commercially available epoxy resins such as bisphenol-epichlorohydrin condensates. Finally, currently available emulsified epoxies have stability problems.
The in situ polymerization and molecular enhancement of polyepoxide or diepoxide in water has not been disclosed in the context of coatings, inks, adhesives and sealants applied by brush, roll, spray, and electrodeposition as a viable alternative to the methods and compositions described.
There is very little information in the literature regarding reactions to increase the molecular weight of polyepoxides or diepoxides through homopolymerization or through the reaction between the oxirane and amine hydrogen, or still further through the reaction between the oxirane and ionic compounds such as those generated from sodium, potassium, ammonium hydroxide, etc. Chapter 5 of Lee and Nevil, entitled "Epoxy Resins", describes the many reaction potentials of the oxirane ring but does not discuss or explain possible ionic in situ polymerization.
On the polyamine side, there are a number of severe limitations to the in situ polymerization and molecular enhancement of polyepoxide or diepoxide in water. For example, in order to be water miscible with the water-borne epoxy, the polyamine must be either a water solution, a water emulsion, or a combination of the two. Those skilled in the art, however, recognize that it is extremely difficult to develop stable polyamine emulsions as a result of the very high viscosity of many water-soluble polyamines in the desired molecular weight range.
In the field application of maintenance finishes, the mixed components must be workable for a minimum of four hours and preferably eight hours. Yet, the mixed materials, upon evaporation or removal of water, must cure rapidly.